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Android Reference

SharedPreferencesBackupHelper


android.app.backup

Class SharedPreferencesBackupHelper

  • All Implemented Interfaces:
    BackupHelper


    public class SharedPreferencesBackupHelper
    extends Object
    implements BackupHelper
    A helper class that can be used in conjunction with BackupAgentHelper to manage the backup of SharedPreferences. Whenever a backup is performed, it will back up all named shared preferences that have changed since the last backup operation.

    To use this class, the application's backup agent class should extend BackupAgentHelper. Then, in the agent's BackupAgent.onCreate() method, an instance of this class should be allocated and installed as a backup/restore handler within the BackupAgentHelper framework. For example, an agent supporting backup and restore for an application with two groups of SharedPreferences data might look something like this:

     import android.app.backup.BackupAgentHelper;
     import android.app.backup.SharedPreferencesBackupHelper;
    
     public class MyBackupAgent extends BackupAgentHelper {
         // The names of the SharedPreferences groups that the application maintains.  These
         // are the same strings that are passed to Context.getSharedPreferences(String, int).
         static final String PREFS_DISPLAY = "displayprefs";
         static final String PREFS_SCORES = "highscores";
    
         // An arbitrary string used within the BackupAgentHelper implementation to
         // identify the SharedPreferenceBackupHelper's data.
         static final String MY_PREFS_BACKUP_KEY = "myprefs";
    
         // Simply allocate a helper and install it
         void onCreate() {
             SharedPreferencesBackupHelper helper =
                     new SharedPreferencesBackupHelper(this, PREFS_DISPLAY, PREFS_SCORES);
             addHelper(MY_PREFS_BACKUP_KEY, helper);
         }
     }

    No further implementation is needed; the BackupAgentHelper mechanism automatically dispatches the BackupAgent.onBackup() and BackupAgent.onRestore() callbacks to the SharedPreferencesBackupHelper as appropriate.

    • Constructor Detail

      • SharedPreferencesBackupHelper

        public SharedPreferencesBackupHelper(Context context,
                                     String... prefGroups)
        Construct a helper for backing up and restoring the SharedPreferences under the given names.
        Parameters:
        context - The application Context
        prefGroups - The names of each SharedPreferences file to back up
    • Method Detail

      • performBackup

        public void performBackup(ParcelFileDescriptor oldState,
                         BackupDataOutput data,
                         ParcelFileDescriptor newState)
        Backs up the configured SharedPreferences groups.
        Specified by:
        performBackup in interface BackupHelper
        Parameters:
        oldState - An open, read-only ParcelFileDescriptor pointing to the last backup state provided by the application. May be null, in which case no prior state is being provided and the application should perform a full backup.
        data - An open, read/write BackupDataOutput pointing to the backup data destination. Typically the application will use backup helper classes to write to this file.
        newState - An open, read/write ParcelFileDescriptor pointing to an empty file. The application should record the final backup state here after writing the requested data to the data output stream.
      • finalize

        protected void finalize()
                         throws Throwable
        Description copied from class: Object
        Invoked when the garbage collector has detected that this instance is no longer reachable. The default implementation does nothing, but this method can be overridden to free resources.

        Note that objects that override finalize are significantly more expensive than objects that don't. Finalizers may be run a long time after the object is no longer reachable, depending on memory pressure, so it's a bad idea to rely on them for cleanup. Note also that finalizers are run on a single VM-wide finalizer thread, so doing blocking work in a finalizer is a bad idea. A finalizer is usually only necessary for a class that has a native peer and needs to call a native method to destroy that peer. Even then, it's better to provide an explicit close method (and implement Closeable), and insist that callers manually dispose of instances. This works well for something like files, but less well for something like a BigInteger where typical calling code would have to deal with lots of temporaries. Unfortunately, code that creates lots of temporaries is the worst kind of code from the point of view of the single finalizer thread.

        If you must use finalizers, consider at least providing your own ReferenceQueue and having your own thread process that queue.

        Unlike constructors, finalizers are not automatically chained. You are responsible for calling super.finalize() yourself.

        Uncaught exceptions thrown by finalizers are ignored and do not terminate the finalizer thread. See Effective Java Item 7, "Avoid finalizers" for more.

        Overrides:
        finalize in class Object
        Throws:
        Throwable


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